Electropneumatic control of atmospheric conditions



Sept 19, 1950 l. l. DAVIES 2,523,198

ELECTROPNEUMATIC CONTROL or ATMOSPHERIC counn'xous Filed Feb. 21, 1946 2Sheets-Sheet l Fial 3mm Idris LDauies 8 am,&f.,

y m w 2 5 m 1 a w 9 9 m0 .1 3 h I n Wh m: S 2 m g \o: M a m M 2 d I l.'l. DAVIES m: A NOH v9 m5 0 POM m vo AQOH QOH ELECTROPNEUMATIC CONTROL OFATMOSPHERIC CONDITIONS Sept. 19, 1950 Flled Feb. 21, 1946 Patented Sept.19, 1950 ELECTROPNEUMATIC CONTROL OF ATMOS- PHERIC CONDITIONS Idris IvorDavies, Milwaukee, Wis., l-lsignor to pany, Milwaukee. Wis., a

Johnson Service Corn corporation of Wisconsin Application February 21,1948, Serial No. 849.246

7 Claims. I

This invention relates to the control of temperature or humidity orother atmospheric condition.

The invention combines the rapid and precise sensing characteristics ofvariable resistance elements with the smoothly graduated and powerfulmotor action of pneumatic systems.

In addition, the invention affords compensation (to stabilize thecontrol point and prevent hunting) adjustment of sensitivity withpossible conversion from graduated action to on and 0115 control; andready reversibility of action to afford direct action, or alternativelyreverse action.

Indeed the instrument is so adaptable and so easily adjusted thatvarious sensitive elements such as those responsive to temperature orrelative humidity may be interchanged in the same sensing circuit toproduce diflerent types of thermostat, hygrostat or other instrument.This is of great commercial importance because a single basic instrumentis adaptable to a wide range of uses, by simply including a particularsensitive element and appropriate graduated scales for certainpotentiometers.

While compensation has heretofore been applied to bridge circuits usedas a control device, rebalancing was accomplished by one or moreadjustable rheostats whose performance was uncertain because of inherentfriction, and because of changes caused by wear. A feature of thepresent invention is a rebalancing transformer which is subject to smallfriction and negligible wear, and which for these and other reasonsaffords remarkably precise compensation. This may be incorporated in thebridge, or maybe interposed between the output terminals of the bridgeand the device which the bridge controls.

Another feature is the use on the pneumatic end of two relays each withleak port control, one relay being confined to admission functions andthe other to exhaust functions. In this way the air end is caused togive graduated responses in reverse directions to two types of signalaiforded by the sensing circuit.

Preferred embodiments of the invention will now be described byreference to the accompanying drawing, in which:

Fig. 1 is in part a diagram and in part a sectional view of the relaymechanism;

Fig. 2 is a similar view illustrating a modification.

Electrical system Referring to Fig. 1, the control circuit illustratedin the drawing consists of an alternating current bridge. including abalancing transformer incorporated in the bridge; a phase discriminatorfor sensing the direction of unbalance of the bridge on either side ofthe null point: a differential relay operated by the discriminator inaccordance with the direction of unbalance; and a power transformer forenergizing the circuit.

The sensitive element I is a device having electrical resistance whichchanges in value with changes in the condition being sensed, such astemperature or relative humidity. Such devices are known and need not bedescribed in detail. The sensitive element l is connected in a bridgearrangement aving a pair of input terminals A-B and a pair of outputterminals (3-D. One end oi the element l is connected to the terminal Dwhile the other end is connected to one end of a potentiometer 2 whichhas its other end connected through resistance 3 to terminal 0. Themovable contact In. on potentiometer 2 is connected to input terminal A.Thus the arm AC of the bridge is formed'of resistance 3 and the upperportion of the potentiometer 2 connected in series, while the arm AD isformed of the sensitive element i and the lower portion of potentiometer2 connected in series. The arm CB of the bridge includes in serialcircuit relation secondary winding Ia of a balancing transformer I, aresistance 4 and the upper portion of potentiometer I which has itsmovable contact Ia connected to bridge terminal B. The bridge arm DBincludes in serial circuit relation secondary winding lb of thebalancing transformer, resistance i and the lower portion ofpotentiometer 5. Balancing transformer I also includes a primary winding'Ic arranged between secondary windings Ia and lb on a non-metallictubular support, and a magnetic core Id mounted on a sliding rod 1c isarranged to slide axially with respect to the transformer coils. Thecore id is composed of compressed powdered iron (polyiron or theequivalent). Core Id is shorter than the length of la, lb and 1ccombined and preferably it is slightly longer than the primary 1c.

The primary winding la of a coupling transformer l is connected acrossthe output terminals C--D of the bridge, and the secondary winding Ob ofthis transformer is connected to the grid elements of a duo-triodevacuum tube I. This tube is of known construction and involves a cathodeheater to, two cathodes Ob, lb, two grids 00, 9c and two plates Id andId.

A power transformer i0 energized from a suitable source of alternatingcurrent is provided with a secondary winding Ila for energizing thecathode heater 9a of the tube 9, and another secondary winding Iflbenergizes the bridge circuit by connections to input terminals A and B.A potentiometer II is connected across one of the secondary windings,for example winding IIIb, and the variable contact I Id of thispotentiometer is connected to one terminal of the primary winding Ic ofbalancing transformer I, while the other terminal of the primary winding10 is connected to one of the outer terminals of potentiometer II, thusproviding for variable energization of winding 10.

Transformer I is provided with a secondary winding Illc to supply abiasing potential to the grids of tube 9, and another secondary windingIlld supplies current to the plate elements of the tube 9 through adivided circuit each path of which includes a coil of a differentialrelay. One terminal of winding IIlc is connected to the cathode elementsof tube 9, and this connection may also be grounded as at Ga. Apotentiometer I2 is connected across winding I00, and the variablecontact I2a thereof is connected to the midpoint of a resistance pathbridged across the secondary winding 81) of transformer 8 and consistingof resistance elements I3 and I3a connected in series. It will beunderstood that this resistance path may be eliminated, and theconnection from contact I2a may be made to the mid-point of secondarywindin 81). Thus, potentiometer I2 serves to apply an adjustable biasingpotential to both grids of tube 9 with respect to the cathode elements.

One terminal of secondary winding I0d is connected to the cathode leadof tube 9, and the other terminal is connected to the variable contactI40. on potentiometer I4. From this point the circuit of winding Inddivides, one half passing through the left portion of potentiometer I4,through coil I5a. of differential relay DR, and through one pole of areversing switch IE to plate 9d of tube 9. The other circuit iscompleted through the right half of potentiometer I4, through relay coilI5b and through the other pole of switch I6 to plate 9d of tube 9.Switch I6 serves to reverse the connections of the plate elements oftube 9 with respect to the coils of the differential relay DR for apurpose to be described later.

A related switch IEa is used to produce a corresponding reversal of theconnection to winding 'Ic.

Relay coils I5a and I5!) are shunted by condensers Ila and Ilb to reducechattering of the armature I5c of the relay. For the same purpose thepole pieces of the differential relay DR are slotted under the armatureI50 and provided each with a shading coil Ifla, I8b, comprising a ringof copper.

Pneumatic system The pneumatic system is of the leak port type soarranged as to be strictly selective in action, and having a branch linein which pneumatic pressure is varied to actuate the controlled device.

When the electric system is in balance so that the armature I5c is inits mid-position the branch line pressure must be stable. The best wayto assure this is to use two leak ports one of which can only increasethe pressure in the branch line and the other of which can only decreasethis pressure, and actuate the leak valves selectively each from aneutral position.

This requires two relays, a supply relay 2I and a discharge relay 22having leak ports 23 and 24, respectively, with gravitating valve lids29 and 29.

Adjusting screws, clearly shown in the drawing are provided, and theparts are so set that when armature I5c is in its mid-position both leakports are just open wide. Displacement of the armature in oppositedirections permits one or the other lid to close its leak port.

The main air connection, indicated by a legend supplies air at 15 p. s.i. gage pressure past throttle valves 21 and 28 to the pressure chambers29 and 30 of relays 2| and 22. Main air is also supplied freely tosupply chamber II of relay 2I, which is interposed in the path to valve28. Leak port 23 vents chamber 29 and valve 21 is so set that thechamber will be substantially completely vented when the leak port iswide open. Leak port 24 vents chamber 30 and the adjustment of valve 28is similar.

The bottom of chamber 29 is separated by a differential flexiblediaphragm 33 from the branch line chamber 35 and the bottom of chamber30 is separated by a flexible diaphragm 32 from atmospheric chamber 34.Branch line chamber 35 in relay 2I is connected with branch line chamber36 in relay 22. When diaphragm 33 is forced down by rising pressure inchamber 29 induced by closure of leak port 23, it opens spring closedsupply poppet valve 31 and admits main air to branch line chamber 35.When diaphragm 32 is forced down by rising pressure in chamber 30induced by closure of leak port 24 it opens spring closed exhaust poppetvalve 38 and exhausts branch line chamber 36 to atmospheric chamber 34.

Since the branch line 39 is connected to chambers 35 and 3B the relaysact selectively to raise and to lower branch line pressure. When bothrelays are inert the branch line pressure is static. The branch lineleads to a spring biased pressure motor 49 connected to adjust a valve,damper or other instrumentality not shown, but used to control anatmospheric characteristic, for example, temperature, relative humidityor pressure.

Connected with the branch line 39 is a bellows motor 4| in which branchline pressure acts in opposition to spring 42. Motor H is connected tostem 1e and consequently shifts core Id of the balancing transformer.The characteristics of spring 42 are such that when the motor I is inits mean position the line pressure then acting in motor 4I willsubstantially center the armature Id.

Windings I00 and Ind must be connected so that the biasing potentialapplied to the grids of tube 9 from potentiometer I2 is opposite inphase with respect to the operating potential applied to the plateelements from the winding Illd. The voltage supplied by winding IIIc issuch that by moving the contact I2a to the extreme lefthand position,the tube 9 is biased past the cutoff point. The biasing potential may bereduced by moving the contact I20, towards the right and it reaches zeroin the extreme righthand position.

As explained above, the bridge A-B-C--D is energized from winding IIIbby connections to the points A-B. If the arms of the bridge are inbalanced relation, no potential diiference will appear between theoutput terminals CD, but if sensitive element I has a value which causesits arm to be unbalanced with respect to the other arms, a potentialdifference will appear across the terminals CD and it will have adefinite phase relation with respect to the operating potential suppliedto the tube 9 from the plate winding Ind. This potential difference willenergize transformer 8 and impress signal potentials of oppositepolarities on the grids 9c and 9c of tube 9. Thus, one grid of tube 9will be energized by a signal current having the same phase relation asthe voltage impressed upon the plate in the same section of the tube,while the other grid will be energized by a signal current havingopposite phase relation with respect to the voltage impressed on theassociated plate. If the resistance value of th element I is now changedto establish a balanced condition in the bridge, no potential differencewill appear across the output terminals CD, and no signal potential willbe impressed on the grids of tube 9. If the resistanc of element I isnow changed to unbalance the bridge in an opposite direction from theformer condition of unbalance, then a potential difference will appearacross terminals CD but will be 180 out of phase with respect to theunbalance potential previously obtained, and the two signal potentialsimpressed on the grids 9c and 90' will be reversed in phase.

With the bridge in balanced condition, and with potentiometer I2adjusted to supply a biasing potential less than the cut-off value, bothsections of tube 9 will conduct current during the positive alternationsof the voltage supplied from winding Illd and will energize coils I51:and Ib of the differential relay DR. If the two sections of tube 9 areidentical and the circuits of the two relay coils have the samecharacteristies, the two currents will be equal, but in actual practiceit is not likely that the two sections of the tube will be identical orthat the two coil circuits will be the same. The potentiometer I4 isprovided for the purpose Of compensating for differences in the tubesections or in the coil circuits, or both. By adjusting the contact Ilaon the potentiometer, a condition of balance may be obtained in therelay DR.

Assuming a condition of balance to exist in the bridge, an increase inthe resistanceof element I will unbalance the bridge and cause signalsof opposite phase relation to be applied to the grids 9c and 9c of tube9. In one section of the tube, the signal voltage will add to thebiasing voltage supplied from potentiometer I2 and will cause a decreasein the plate current which energizes one of the windings of relay DR. Inthe other section of the tube, the signal voltage will be opposed to thebiasing voltage supplied from pctentiometer I2 and an increase in platecurrent will flow in this section of the tube and in the correspondingrelay winding. Thus the armature I 50 of relay DR will be operated inone direction. Assuming now that the resistance of element I changes inthe opposite direction from that just stated, the resulting signalsimpressed on the grids of tube 9 will be reversed in phase, and theconditions of operation of the two tube sections will reverse; that is,the relay winding which formerly was energized by a low value of currentwill now be energized by a high value of current and the other relaywinding will receive low current, with the result that the armature I5cwill be operated in the reverse direction. Thus, the tube 9 serves tosense the direction of unbalance of the bridge and operates thedifferential relay DR accordingly.

Motion of armature I5c in one or the other direction from the.mid-position shown in the drawing causes one or the other of lids 25 or25 to close the related leak port, and thus through 6 operation ofrelated relay 2| or 22 cause pressure in branch line 39 to rise or fall.The motor II responds to this change of pressure and actuates somedevice, such as a heater, cooler or humidity or pressure controller tocorrect the condition affecting element I.

The foregoing description of operation disregards the function of thebalancing transformer I. This transformer is provided for the purpose ofintroducing balancing voltages into two arms of the bridge for thepurpose of re-establishing a balanced condition in response to changesin a condition being controlled, or more specifically, in response tothe regulatory pressure in branch line 39. I

With the movable core Id positioned at the center of the transformer,equal voltages are induced in the secondary windings Ia and 1b from theprimary winding 10, and these windings are connected in the bridgecircuit in such direction that these voltages are opposed to each otherwith respect to the output terminals CD. Accordingly, with the core inits central position, the balancing transformer will not affect theoperation of the system which is as described above. It will beunderstood that windings Ia and lb are formed of an equal number ofturns and are preferably formed of a small number of turns such that theinductance of these windings has no appreciable effect upon the phaserelation of the currents in the arms of the bridge.

If the core 1d is moved away from its central position so that itextends into one secondary winding to a greater extent than into theother, the voltage induced in the first secondary winding will begreater than in the second, and a potential difference will appearacross the terminals CD. If the core is moved away from its centralposition in the opposite direction, the potential difference appearingacross the terminal CD will be of opposite phase. Thus, if the bridgearms are unbalanced with respect to current supplied across the inputterminals AB, in consequence of a change sensed by element I, acondition of balance may be re-established by moving the core 1d in adirection such that the voltage supplied from the balancing transformerI will oppose and neutralize the output voltage due to the unbalance ofthe bridge. By properly connecting the core id to be moved in responseto a change of branch line pressure, the balancing transformer I willfunction as compensating means.

The sensitivity of the balancing transformer I is significant as to thedegree and character of this compensation and is controlled byadjustment of the potentiometer II which energizes the primary winding10. By moving the contact IIato the lefthand position, the energizingcurrent is reduced to zero, and the sensitivity of the transformer isalso reduced to zero. When the contact I Ia is moved to the right, thesensitivity of the balancing transformer is increased and in proportionto the current supplied to the primary winding lc. Stated differently,the greater the current supplied to the winding lo, the greater will bethe resulting counterbalancing voltage supplied by the transformer I fora given movement of the core Id from its center position.

Adjustment of the value of the condition to be maintained is secured byadjusting the position of the contact So on potentiometer 5 whichdetermines the amount of unbalance of the bridge with respect to theinput terminals AB. Potentiometer 5 may be provided with a scalecalibrated in terms of temperature, humidity or other terms.Compensation for various lengths of line connecting element l with thebridge circuit may be obtained by adjusting the contact In onpotentiometer 2. If a type of sensitive element l characterized by alarge change of resistance in response to a small change of thecondition sensed is employed, resistors 4 and 6 will not be required.The line balancing contact 2:; on potentiometer 2 could then also beeliminated, since the line resistance would be negligible with respectto the resistance change occurring in the element l. Resistors 4, 6, andpotentiometer 2 will be required where element 1 has a low temperaturecoeillcient of resistivity. However, resistance units which arecharacterized by a high change of resistance in response to a smallchange of temperature are well known in the art.

Potentiometer l2 provides an adjustment of the differential response ofthe system. By decreasing the biasing potential to zero, only a smallchange in the controlled condition is required for changing the bridgefrom one condition of unbalance to an opposite condition of unbalance,and the null interval will be very short and will not enter into thecontrol cycle. With a comparatively large biasing potential applied tothe grids of tube 9, a greater change in the condition being controlledis required to overcome this biasing potential to produce operation ofthe differential relay in one direction or the other; the null intervalis greatly lengthened, and there is a greater difference in the value ofthe condition required for operating relay DR in one direction than thatrequired for operating the relay in the opposite direction.

Reversing switches 16 and lta are provided to adapt the system fordirect or reverse operation. That is to say, they reverse the directionin which pressure in branch line 39 changes in response to a change ofcondition affecting resistance element l. The two switches could bemechanically connected to operate in unison.

In practice of the invention it is desirable to ground one point of thebridge, for example, terminal A may be grounded as at G, and it is alsodesirable to ground the cathodes of tube 9 as at Ga. These two groundedsections of the circuit are electrically isolated from each other by thetransformer 8.

It will be observed that in Fig. l the rebalancing transformer isincorporated in the bridge and actually rebalances the bridge proper. Anequivalent effect can be had by interposing a rebalancing transformerbetween the output terminals of the bridge and the coupling transformer.To illustrate this possibility and for the purpose of illustrating adifferent form of rebalancing transformer, Fig. 2 has been included.

Modification illustrated in Fig. 2

In this view parts that generally correspond with parts on Fig. 1 aregiven the same reference numeral increased by one hundred.

In Fig. 2 A and B represent the input terminals of the bridge and C andD the output terminals thereof. Examination of the circuit will indicatethat basically it is similar to the original circuit, but the windingslllla and Nb of the balancing (off null) transformer are not included inthe bridge proper but are interposed between the output terminals C andD and the primary llna of the coupling transformer.

The function of these windings is to cancel the effect of unbalance ofthe bridge as contradisall) tinguished from what might be described asrebalancing the bridge itself. The rebalancing transformer includes acore Ill] comprisinl stack of thin silicon steel laminations. The movingcore lflld is composed of similar laminations and is pivoted to swingaround the fulcrum under the influence of the bellows motor ill. Theclearance between the member "1d and the core II"! is small, being about.004".

The primary winding "1c is on the center arm of the core and windings"In. and "1b are on the end arms of the core. The primary winding Ill'lcobtains its current from the'vacuum tube heater winding Hlla under thecontrol of potentiometer Illa.

The reversing switch Ilia is provided for the same purpose as switch aof Fig. 1. When the moving core lll'ld is in its midposition thereluctance of the magnetic circuit coupling secondary 101a to primaryllllc is equal to the reluctance of the magnetic circuit couplingsecondary llllb to primary lllc. Consequently, the currents induced inthe secondary coils are equal. Since the secondary coils are connectedin series in the output circuit of the bridge, and since they arereversed in phase with respect to one another, they will introduce norebalancing effect in the output circuit of the bridge when core "lid isin its centered or normal position. If the core is moved away from itscentered position in one or another direction, the differential currentwill be caused to flow in the output circuit of the bridge and its phasewill reverse as the moving core lflld crosses its normal position. Themagnitude of the current will vary according to the displaoement ofmember l0ld from its normal midposition. The remainder of the circuitconforms to the showing in Fig. 1 and requires no detailed discussion.

Two embodiments of the invention have been describedin considerabledetail in order to emphasize the versatility of the rebalancingtransformer which may take different forms and which may be variouslyconnected with the bridge circuit. Consequently, modifications withinthe broad scope of the claims are possible and are contemplated.

What is claimed is:

1. The combination of an alternating current bridge, including anelement responsive to a con dition to be sensed arranged to unbalancethe bridge in opposite phases upon departure of said condition inopposite directions from a predetermined normal value; aphase-discriminator comprising at least one electron tube arranged torespond selectively to opposite departures of said bridge from balance;a motor responsive to a variable pressure and adapted to control thesensed condition; a source of pressure fluid; electrically operatedvalve means controlled by said phase discriminator and arranged toconnect said motor selectively with said source and with exhaust; andmeans for neutralizing an unbalanced condition of said bridge. saidmeans comprising an adjustable transformer having a shiftable armature,and an independent motor subject to the pressure in the first namedmotor and connected to shift said armature.

2. The combination of an alternating current bridge, including anelement responsive to a condition to be sensed arranged to unbalance thebridge in opposite phases upon departure of said condition in oppositedirections from a predetermined normal value; a phase-discriminatorcomprising at least one electron tube arranged to respond selectively toopposite departures of said bridge from balance; a motor responsive to avariable pressure and adapted to control the sensed condition; a sourceof pressure fluid; electrically operated valve means controlled by saidphase discriminator and arranged to connect said motor selectively withsaid source and with exhaust; an adjustable transformer forming part ofsaid bridge and adjustable to rebalance the same; and motor meansresponsive to the pressure in the first named motor to adjust thetransformer to effect rebalance of the bridge.

3. The combination of a bridge'having four arms connected between a pairof input terminals and a pair of output terminals; a source ofalternating current connected to said input terminals; an elementresponsive to a condition to be sensed connected in one arm of saidbridge; a phase discriminator connected to the output terminals of saidbridge for sensing unbalance of said bridge in opposite directions;motor means for controlling the magnitude of the condition being sensed;means controlled by said phase discriminator for energizing said motormeans to increase or decrease said condition according to the unbalanceof said bridge; transformer means for normally inducing alternatingcurrent voltages of opposite phase into two arms of said bridgeconnected in series across said output terminals; and movable meanscontrolled in accordance with the energization of said motor for varyingthe magnitudes of said induced voltages in opposite directions.

4. A combination according to claim 3 wherein said transformer meanscomprises a transformer having a primary winding energized from saidsource of alternating current and two secondary windings arranged onopposite sides oi! said primary winding and connected in said two armsof said bridge, and a movable magnetic core for varying the couplingbetween said primary winding and said two secondary windings in oppositedirections 5. The combination of a bridge having four arms connectedbetween a pair of input terminals and a pair 01' output terminals; asource of alternating current connected to said input terminals; anelement responsive to a condition to be sensed connected in one arm ofsaid bridge; a phase discriminator connected to the output terminals ofsaid bridge for sensing unbalance of said bridge in opposite directions;motor means for controlling the magnitude of the condition being sensed;means controlled by said phase discriminator for energizing said motormeans to increase or decrease said condition according to the unbalanceof said bridge; transformer means for normally inducing alternatingcurrent voltages of opposite phase into two arms of said bridgeconnected in series across said output terminals; adjustable means forvarying the energization of the primary winding oi said transformermeans; and movable means controlled in accordance with the energizationof said motor for varying the magnitudes of said induced voltages inopposite directions.

6. The combination of a bridge having four arms connected between a pairof input terminals and a pair of output terminals; a source ofalternating current connected to said input terminals; an elementresponsive to a condition to be sensed connected in one arm of saidbridge; a phase discriminator connected to the output terminals of saidbridge for sensing unbalance of said bridge in opposite directions;motor means for controlling the magnitude oi the condition being sensed;means controlled by said phase discriminator for energizing said motormeans to increase or decrease said condition according to the unbalanceof said bridge; transformer means for normally inducing alternatingcurrent voltages of opposite phase connected in series in the circuitwhich connects the output terminals of said bridge with the phasediscriminator; adjustable means for varying the energization of theprimary winding of said transformer means; and movable means controlledin accordance with the energization oi. said motor for varying themagnitudes of said induced voltages in opposite directions.

7. The combination of a bridge having four arms connected between a pairof input terminals and a pair of output terminals; a source ofalternating current connected to said input terminals; an elementresponsive to a condition to be sensed connected in one arm of saidbridge; a phase discriminator connected to the output terminals of saidbridge for sensing unbalance of said bridge in opposite directions;motor means for controlling the magnitude of the condition being sensed;means controlled by said phase discriminator for energizing said motormeans to increase or decrease said condition according to the unbalanceof said bridge; transformer means for normally inducing alternatingcurrent voltages of opposite phase in the output circuit of said bridge;adjustable means for varying the energization oi' the primary winding ofsaid transformer means; and movable means controlled in accordance withthe energization of said motor for varying the magnitudes of saidinduced voltages in opposite directions. 7

IDRIS IVOR DAVIES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 788,278 Porter Apr. 25, 19052,080,212 Otto May 11, 1937 2,262,173 Fischer Nov. 11, 1941 2,358,103Rydner Sept. 12, 1944 2,363,690 Razek Nov. 28, 1944 2,390,425 Crum Dec.4, 1945 2,403,917 Gille July 16, 1946 2,430,757 Conrad Nov. 11, 1947

